An LED, as used herein, is a semiconductor light source for generating a light at a specified wavelength or a range of wavelengths. LEDs emit light when a voltage is applied. LEDs have increasingly gained popularity due to favorable characteristics such as small device size, long lifetime, efficient energy consumption, and good durability and reliability. In recent years, LEDs have been deployed in various applications, including indicators, light sensors, traffic lights, broadband data transmission, and illumination devices. For example, LEDs are often used in illumination apparatuses provided to replace conventional incandescent light bulbs, such as those used in a typical lamp.
One of the performance criteria for LEDs is light extraction efficiency. For example, it is desired that the light output for an LED (e.g., measured in terms of optical power) be as great as possible for any given LED. However, existing LEDs often have poor light extraction efficiency, or may require expensive tools and/or long processing times to improve their light extraction efficiency.
Therefore, while conventional LEDs have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect. It is desired to improve the light extraction efficiency for LEDs without requiring expensive equipment or long processing times.